The present invention relates to a hydraulic control system for an automatic transmission.
It is known that, in a three speed automatic transmission, a third speed ratio is established when an engine is subject to no load (that is, when the depression degree of an accelerator pedal is zero or almost zero), thereby minimizing a creeping i.e., a phenomena wherein a vehicle moves at a slow speed due to a drive caused by the engine idle. If this technology is applied, for example, to a four speed automatic transmission having an overdrive, it turned out to establish a four speed ratio under no engine load condition. This results in the highest speed ratio, i.e., the overdrive, being established when the accelerator pedal is released in order to decrease the vehicle speed while the vehicle is travelling through a winding road in second or a third gear bringing about a situation in which driving power is lost rapidly, thus increasing the tendency of the vehicle to spin.